Optical discs, such as compact discs (CD) and digital versatile discs (DVD) are forms of computer readable media which provide extensive storage for digital information. One side of an optical disc may contain data and is referred to as a data side. The data side may be read only, or may also be written to. The other side of the optical disc that does not contain data may provide for a label and is referred to as the label side. In particular cases, a side or both sides may provide for both data and a label.
An optical disc drive (ODD) of a computer may be used to read from and may write to a data side of an optical disc. An optical pickup unit (OPU), included within the optical disc drive, is configured with a laser and sensors adapted for reading, and possibly writing, data. Various ODDs and OPUs are available, and are manufactured to specifically read and write to the data side of optical discs.
Using emerging technology, the OPU assembly may be used to produce an image on the label surface of an optical disc configured for such a labeling process. Producing the image includes defining tacks which are concentric circles of the optical disc where the image is written, and focusing focal optics of a laser beam that performs the actual printing of the image on the optical disc.
An ODD typically includes a voice coil motor (VCM) configured as a sled motor that moves an OPU assembly in a radial direction to a position that is adjacent particular tracks of the optical disc. An OPU assembly may also include a VCM configured as a focus motor that moves focal optics to a particular distance orthogonal to a surface of the disc such as a height above or below the disc, to focus a laser beam for labeling. The VCMs are responsive to an input signal (voltage or current) and move to a particular location when a particular input signal is applied. Therefore, when an input signal is applied to the sled VCM, the OPU assembly is moved adjacent to a particular track. Likewise, when an input signal is applied to the focus VCM, the focal optics are moved to a particular focus position. The VCMs are typically calibrated to move a particular distance when a particular input signal is applied. The calibration is performed at a particular temperature.
However, a VCM includes metal windings whose electrical conductivity is affected by temperature changes. Therefore when the VCM is heated, the resistance of the metal windings goes up and electrical conductivity increases. Since a VCM is calibrated at a particular temperature to move a particular distance based on a particular input signal, not accounting for temperature changes can result in inaccurate positioning. For example, if a VCM is operated at a temperature different from the calibration temperature, a particular input signal may move the OPU assembly to an incorrect track position or the focal optics to an incorrect focus position.
Accordingly, a need exists for the present invention.